• First developed in the 1600’s in Europe.
• Gave rise to the Cell Theory in 1839
• The Cell Theory states:
• (1) All organisms are composed of one or
• (2) The cell is the structural unit of life
• (3) Cells can arise only by division from a
What can a Microscope tell us
• Allows user to view the morphology of a
• Typically seen are nucleus, plasma
membrane, cell wall and chloroplasts in
• Cells are viewed as two dimensional even
though cells are really three dimensional
• Difficult to view details in cell because a
cell lacks color
• Chemical dyes are used to give cells color
and to make parts of a cell visible
• Dyes can be used to stain DNA, proteins,
specific cellular structures
• Problem light microscope can resolve
features who size is not less than 0.2 mm
• Resolution is the ability to discern two
objects as being separate
• Unfortunately, most organelles in a cell are
less than 0.2 mm in size
• In the 1950’s the transmission electron
microscope was invented.
• This microscope has a resolution of 10 –
15 Angstroms. (One Angstrom is ten
• This allows organelles to be viewed.
• Yet in spite of the electron microscope the
function of a cell is not revealed!
• The problem is not the microscope but the
information that it yields
• The function of a cell is revealed through
• In order for a cell to be alive it must be
acquire and use energy
• Possess a genetic code and have a way to
• Cell must be able to replicate
• Respond to stimuli
Eukaryote vs Prokaryote
• Using a light microscope it is possible to
determine if a cell has a nucleus or not.
• Those cells who do have a nucleus are
call eukaryotes and those without a
nucleus are prokaryotes.
• Typically, prokaryotes are bacteria and the
cells do not work together
• Eukaryotes work together and comprise
complex organisms like us.
• Eukaryotes are specialized cells that
require resources from other cells to
• Typically eukaryotes have much greater
energy needs than prokaryotes.
• To satisfy the energy needs as well as the
specialization eukaryotes have organelles.
• Organelles are membrane bound
structures that perform a specific task.
Prokaryotes are not evolutionay
ancestors of eukaryotes
• Eukaryotes and prokaryotes are very
• Prokaryotes have a single RNA
• Eukaryotes have three
• Prokaryotes do not have RNA splicing
• The ribosomes in prokaryotes and
eukaryotes are different
• Resemble bacteria found in extreme
environments on the earth
• Examples include methanogens which
• We will talk more about organelles later in
Infectious agents that are not
• Viruses, viroids, and prions are infectious
agents, but are not cells
• In fact, most people would agree that
these infectious agents are not alive.
• As previously mentioned a cell must be
able to perform specific processes to be